Loss-of-function GBA1 mutations in Gaucher disease result in increased risk for Parkinson's disease (PD). Glucocerebrosidase (GCase) normally breaks down a lipid called glucosylceramide (GluCer) that accumulates due to decreased GCase activity. Previous data have indicated that GluCer directly interacts with alpha-synuclein, the main component of Lewy body inclusions; the GluCer-alpha-syn interaction stabilizes alpha-synuclein, causing it to accumulate into aggregates (clumps). Glucosylceramide-reducing agents are expected to destabilize toxic alpha-synuclein aggregates, rendering them amenable to degradation through cellular clearance systems.
GluCer-reducing agents will prevent the accumulation of pathological alpha-synuclein by increasing its degradation rate, therefore providing a therapeutic benefit.
Well-established small molecule GluCer-reducing agents will be utilized in PD midbrain neuronal models. These cells will be derived from induced pluripotent stem cells ("man-made" stem cells that can become other cell types) that have been reprogrammed from fibroblasts from individuals with PD who have genetic mutations in GBA1 or alpha-synuclien; neuronal models have been fully characterized and demonstrate the presence of pathological a-synuclein. Cultures will be treated with GluCer-reducing agents and analyzed for reductions in pathological alpha-synuclein by amyloid-specific staining (cell labeling) and sequential biochemical extractions. In addition, we will determine if alpha-synuclein reduction reverses downstream toxicity, including lysosomal dysfunction and neuron viability, with our established assays.
Impact on Diagnosis/Treatment of Parkinson's disease:
This study will determine the effect of reducing GluCer on alpha-synuclein pathology in neurons that naturally accumulate alpha-synuclein through genetic mutations. If successful, these data would suggest that manipulating the GluCer metabolizing pathway holds promise as a disease-altering therapeutic for PD. GluCer-reducing therapies are currently approved for the treatment of Gaucher disease; therefore, outcomes of this study have potential to rapidly impact Parkinson's disease patients.
Next Steps for Development:
GluCer-reducing small molecules will be tested in vivo for the ability to reduce pathological alpha-synuclein, using pre-clinical models of PD and Gaucher disease that accumulate alpha-synuclein.
In this study, we aimed to reduce the production of glucosylceramide (GluCer), a substance that builds up in the body of people with changes (mutations) in the GBA1 gene, which have been linked to Parkinson's disease (PD) and Gaucher disease. We found that reducing the production of GluCer could reduce toxic clumps of alpha-synuclein -- the hallmark of PD -- in midbrain nerve cells generated from induced pluripotent stem cells (iPSCs). We tested iPSCs from people with and without GBA1 mutations and found similar reductions in GluCer production in both types of cells, indicating the potential for therapies based on GluCer reduction for PD with an unknown cause. GluCer reduction improved alpha-synuclein properties but not the health of nerve cells in all iPSC cell types tested. GluCer reduction in control nerve cells did not affect the health of nerve cells, properties of alpha-synuclein or glucocerebrosidase activity. To determine whether GluCer reduction stimulates autophagy -- the process of cellular self-eating -- we examined autophagy in healthy, control cells treated with drugs that slow GluCer production and found no significant change. Our results indicate that GluCer reduction may have therapeutic value in reducing pathological alpha-synuclein in people with Parkinson's.
Presentations & Publications
Zunke F, Moise AC, Belur NR, et al. Reversible Conformational Conversion of alpha-Synuclein into Toxic Assemblies by Glucosylceramide. Neuron. 2017. PMID: 29290548.
Zunke F, Moise AC, Belur N, et al. Formation of toxic a-synuclein assemblies can be reversed by glucosylceramide reduction in human midbrain dopamine neurons. Presented at: 13th International Conference on Alzheimer's & Parkinson's Disease; March 29 - April 2, 2017; Vienna, Austria.
Moise AC, Zunke F, Toker NJ, Dzaferbegovic H, Mazzulli JR. Induction of a-synuclein aggregates by loss of glucocerebrosidase activity is reversed by glycosylceramide reduction in human midbrain dopamine neurons. Poster presented at: Gordon Research Conference on Glycolipid and Sphingolipid Biology; March 6-11, 2016; Lucca, Italy.